The troposphere is considered as the layer closest to Earth and is also the region where temperatures reliably decrease with altitude. The troposphere is thickest at the Earth’s equator, reaching heights of about 11 miles (17 to 18 kilometers), and this is, therefore, also where you will find the coldest tropospheric temperatures. It might seem rather ironic that, right above the world’s steamiest tropical forests, temperatures can be as low as –110°F (-79°C).